The present invention relates generally to an optical system for delivery of a collimated beam of light in conjunction with automatic equipment and, more specifically, to a laser beam-directing joint for use in the field of robotics.
High powered lasers are ideally suited to be used as a source of heat in various material processing applications which include the vaporization of materials, such as in drilling and cutting operations. Lasers are also applicable to procedures, such as welding or surface cladding of metals, which require the melting of materials. Also, the temperature of solid phase materials can be varied, by use of the laser, in hardening and annealing operations.
The thermal effects which are experienced by materials when exposed to the laser beam are primarily dependent on the intensity of laser energy, the absorptivity of the material and the length of time during which the material is exposed to the laser beam. Precise control over these parameters determines the resulting change in the phase or the state of the material. Usually, when lasers are used in processes such as welding, cutting and surface treatment, the area of the workpiece to be processed is orientated in such a way that it is nearly normal to the laser beam with the beam impinging squarely on its surface. This configuration optimizes the absorptivity of the material and facilitates its heating. Generally, the laser and the workpiece are caused to move relative to each other. This relative motion can be accomplished in two ways. First, the beam can be traversed over a stationary workpiece. Second, the workpiece can be manipulated under a fixed laser beam. The former method requires that the laser beam be moved either by mounting the laser on a movable device or by directing the beam from a fixed laser to the workpiece by use of a movable optical system. The latter method requires the use of a workpiece-manipulating device.
Generally the latter method is employed. Most present systems which use the laser for material processing employ a fixed laser beam along with apparatus that is capable of manipulating the workpiece. This manipulation of the workpiece usually incorporates linear or rotational movement of the part and exploitation of the part's symmetry. Symmetrical or simple parts can be processed by machines having one or two axes of motion, but any moderately complex workpiece requires a part manipulating machine which has the capability of providing four or five axes of motion. The required manipulations of such workpieces, along with the general requirement that the laser beam impinge the working surface normally, are difficult to achieve with currently available part handling devices. Furthermore, these devices are usually made for specific parts and with dedicated hardware. Therefore, they are not readily retooled when changes in part shape and dimension occur. Other disadvantages of this type of equipment are that large, cumbersome parts are difficult to position accurately and repeatedly and have significant inertial effects when moved. Also, due to part geometry, obstructions may occur which prevents a clear "line of sight" between the laser beam source and the working surface of the workpiece.
Machines which are designed to produce a specific product are only economically feasible if a large number of parts are to be produced. Simple economics often preclude smaller batch operations. Therefore, a highly versatile system with laser beam delivery optics is needed which is capable of processing workpieces that have complex shapes and sizes in small batch quantities with minimum required retooling when the configuration of the workpiece changes.
The present invention permits the use of industrial robotic technology to be used in laser beam delivery applications. The use of a number of articulated mirrors allows the laser beam to comply synchronously with movements of the robot's manipulator. Therefore, the manipulator can then deliver a focused beam to any point within the robot's geometric range and move the beam along a contoured path with a controlled velocity.
Recent developments in the field of laser utilizing robotics incorporate an articulated laser-directing arm with mirrors disposed at its joints to reflect the light beam along the arm's segments. An example of recent articulated beam-directing optics is described in "At Coherent: advanced lasers and new ideas in robotics" by Gary S. Vasilash, Manufacturing Engineering, March, 1981, pp. 84-85 in which an optical articulated arm is illustrated and described. This arm provides a light path from a stationary laser to an end-effector which contains beam focusing optics. The end-effector is attached to a robot arm which is capable of automatic operation. The light directing arm and the robot arm are connected only at the end-effector and the light directing arm's joints are each free to move in order to permit the laser directing arm to span the distance between the laser and the point in space at which the robot arm has positioned the end-effector. This configuration is analogous to a dentist's drill-support mechanism in its principle of operation. The drill bit is comparable to the laser system's end-effector and the dentist's arm is analogous to the robot arm. The drill-support mechanism comprises a plurality of articulated joints which can each move in such a way that the linkage system spans the distance between the motor and the dentist's hand.
A limitation of the system described above lies in the relative positions of the light source and the center of the robot's motion. Just as the dentist must avoid turning completely around with the drill in his hand, the robot must be controlled in such a way that its movements do not cause the light directing arm to attempt to extent through the robot itself or its arm. The present invention eliminates this limitation by combining the light directing arm with the robot's arm in such a way that they move synchronously and, thus, are incapable of mutual interference.
Other developments in the field of the adaptation of robotic technology to laser applications are discussed in "Laser Processing at Ford", by Michael Yessik and Duane J. Schmaty, Metal Progress, May, 1975, pp. 210-215. Examples of manipulator systems are discussed in U.S. Pat. No. 3,937,057 issued to Trolle on Feb. 10, 1976 and U.S. Pat. No. 4,221,997 issued to Flemming on Sept. 9, 1980. Other robotic systems are disclosed in U.S. Pat. No. 4,260,319 issued to Motada et al on Apr. 7, 1981, U.S. Pat. No. 4,076,131 issued to Dahlstrom et al on Feb. 28, 1978 and U.S. Pat. No. 4,089,427 issued to Pardo et al on May 16, 1978. Inventions that relate particularly to actuators and joints for robots are discussed in U.S. Pat. No. 3,848,753 issued to Borg et al on Nov. 19, 1974, U.S. Pat. No. 3,777,618 issued to Iwai et al on Dec. 11, 1973 and U.S. Pat. No. 4,096,766 issued to Pardo et al on June 27, 1978.
The present invention, in its simplest form, comprises a joint which is rotatably attached to a support member or arm. A reflective member with a mirror surface is attached to the joint in such a way that the mirror surface is intersected by the axis of motion about which the joint rotates with respect to the support member. By adjusting the angle of the mirror surface with respect to this axis of motion, a collimated beam of light which travels along this axis of motion can be reflected by the mirror surface in any one of an infinite number of directions. When the reflective member is attached to the joint, a specific preselected angle of reflection is determined for the collimated beam of light. It should be apparent that, when the joint member is rotated about the axis of motion, the reflected beam of collimated light is moved in such a way that it describes either a flat or conical surface. When the mirrored surface is disposed at an angle of 45.degree. to the axis of rotation, the reflected beam of collimated light will pass at an angle of 90.degree. to the originating beam and, as the joint is rotated about its axis of motion, the reflected beam will describe a generally flat surface to which the axis of motion of the joint is perpendicular.
If the support member described above is a hollow tube with the joint member rotatably attached to one end, the beam of collimated light can be passed through the support member along its longitudinal axis. It should be understood that this longitudinal axis is also coincident with the axis of motion of the joint. It should be further understood that it is of prime importance to the proper application of the present invention that the beam of collimated light passes along the axis of motion of the joint member. This characteristic permits the joint to be rotated at any angle about the axis of motion while maintaining a clearly predictable path of the reflected laser beam. This attribute also permits an additional support member to be rigidly attached to the joint in such a way that it rotates with the joint about the axis of motion described above. This additional support member allows a second joint to be rotatably attached to it so that a mirror surface of a second reflective member can be positioned within the second joint in such a way that it is intersected by a second axis of motion which lies between it and the mirror surface of the first joint and along which the reflected laser beam passes.
The axis of motion of the optical joint is coincident with that of the robot arm to which it is attached. In a multi-jointed robot, each segment of the robot's arm is associated with a straight segment of the light beam. The arm segment and the beam segment move in synchronism. The robot arm can be attached to a tubular member and optical joint or, alternatively, these light-directing components can be incorporated within the robot arm itself.
It should be apparent that the present invention makes possible the passage of a collimated light beam along the articulated arms of a robot and more synchronously with it. It should further be understood that, by appropriate selection of type and number of the joints described above, a robot can be configured that is capable of delivering a laser beam to virtually any point within its geometric range and at virtually any angle to that point in space.